The use of wireless communication has grown steadily for years, as wireless communication systems offer customers convenience and flexibility. Wireless cellular communication systems have been based on a wide variety of technologies, such as Time Division Multiple Access (“TDMA”), Global System for Mobile communications (“GSM”), Universal Mobile Telecommunications System (“UMTS”), and Code Division Multiple Access (“CDMA”). These technologies have evolved in an attempt to increase the number of subscribers that can be serviced at a given time (capacity) and also to improve the quality of service for subscribers. For instance, in recent years so-called third generation or “3G” cellular systems have been deployed to provide access to fast Internet and video. These include systems based upon standards and/or recommendations such as 3GPP and IMT-2000, which implement wideband CDMA (“WCDMA”) or other high-bandwidth architectures.
Such systems offer customers a wide array of services, from basic voice communication to Short Message text messaging (“SMS”), Multimedia Messaging Service (“MMS”), e-mail access and even video applications. FIG. 1 illustrates a conventional cellular wide-area network implementation 10 in which a number of cells 12 are each served by one or more base stations (“BSs”) 14. Each base station may include a RF (Radio Frequency) transmission section and a baseband section for signal processing, call management, etc. A number of base stations are typically coupled to a mobile switching center (“MSC”) or mobile telephone switching office (“MTSO”) 16. In turn, the MTSO 16 is coupled to other network elements (not shown) and/or to the public switched telephone network (“PSTN”) 18. User devices 20 include wireless telephones, laptop computers, Personal Digital Assistants (“PDAs”) and other devices that have two-way voice, data and/or video capabilities. Such devices are often referred to as mobile units or mobile stations (“MSs”).
As a given mobile station 20 travels or roams across a service provider's network, it typically sends and receives packets of data, including digitized voice, from multiple base stations. At any given time, primary communication (e.g., a voice call) is conducted between the mobile station and one base station, commonly referred to as the “serving base station.” The serving base station may change from a first base station to a second base station as the location of the mobile station changes or other factors impinge on the signal between the mobile station and first base station. This process of switching between base stations is called handoff.
One of the major problems in cellular communication may be the unsatisfactory quality of service for subscribers. The signals transmitted between users' mobile stations and the network's base stations may be affected by a number of different factors, including blockage by buildings or terrain, multipath interference, movement and speed of the mobile station, handoffs between base stations, other mobile stations, etc; other network transmission characteristics, such as delay, jitter and uptime (availability) of the network affect signal quality as well. Furthermore, there is a finite bandwidth available at each base station or for a given cell in the wireless system. Thus, users are often subject to dropped calls and inferior voice quality, in contrast to the general high reliability of landline phone communications with plain old telephone service (“POTS”).
The number of users who can be served by a cell or by a particular base station is impacted by the above mentioned issues and other factors. Service providers and mobile equipment manufacturers have attempted to deal with such issues with a number of different solutions. For instance, a serving base station may require mobile stations to perform power control to limit their transmission power. This helps to reduce the interference presented by transmissions from other mobile stations signals and therefore increase the signal to interference and noise ratio (“SINR”) for other mobile stations. It can also enable more users on the system at a given time.
Mobile stations may also employ improved reception using so-called “RAKE” receivers to handle multipath propagation. See, for instance, “WCDMA for UMTS: Radio Access for Third Generation Mobile Communications,” edited by Holma and Toskala, copyright 2000 by John Wiley & Sons, Ltd., the entire disclosure of which is hereby incorporated by reference herein. Another useful reference is “CDMA: Principles of Spread Spectrum Communication,” by Andrew Viterbi, copyright 1995 by Addison-Wesley Publishing Co., the entire disclosure of which is hereby incorporated by reference herein.
Another solution to make a communication channel more efficient implements speech coding to reduce the amount of data that must be sent in order to reliably reproduce a user's voice. A general treatment of speech coding may be found in “Mobile Communication Systems,” by Parsons and Gardiner, copyright 1989 by Blackie and Son Ltd., the entire disclosure of which is hereby incorporated by reference herein.
Speech coding in mobile telephony applications is typically done using a codec (coder/decoder). Voice codecs or voice coders (“vocoders”) having varying levels of compression are often employed to reduce the required communication bandwidth by reducing the sampling rate of a voice signal. The terms codec and vocoder are used interchangeably herein.
Most of the frequencies that reproduce speech lie in the range of about 300 Hz to 3400 Hz. A band-limited signal, such as a speech signal, may be reconstructed from digital samples taken at or above the “Nyquist rate,” which is a rate corresponding to two times the frequency bandwidth of the signal. This may require up to 64 Kb/s per user. However some vocoders can provide a reasonably good representation of voice with as little as 2.4 Kb/s of data rate.
Over the years, a number of different techniques have been used in different systems. By way of example only, one technique called code-excited linear prediction (“CELP”) has been implemented by Qualcomm in its “QCELP” vocoders. Another popular technique is called the enhanced variable rate codec (“EVRC”). More recently, a variation called EVRC-B has been implemented in 3G systems. Other techniques include the selectable mode vocoder (“SMV”) and adaptive multi-rate compression (“AMR”).
One of the advantages of vocoders implementing such techniques is that the compression rate may be varied. Variable compression can result in reduced transmission overhead, which, in turn, can enable a service provider to accommodate more users on the wireless system. However, for any given vocoder the higher the compression level and the fewer bits used to represent the information, the less the output sounds like the original input (e.g., the voice of the user). In other words, the fidelity of the coded voice will decrease as the number of bits used to represent the voice decreases. While the user may not notice some degradation in quality, if the bit rate is reduced enough, or if a less robust vocoder is used, at some point the user may become aware of the reduced quality of the call.
Furthermore, in many applications a vocoder may change the bit rate one or more times during a call, and different calls may use different vocoders. Thus, a user may experience varying voice quality in the middle of a call or when making or receiving different calls. This can be frustrating to many users. Unfortunately, in conventional systems the user has no control over which vocoder is used or which level of compression is employed at any given time. Instead, these are typically mandated by standards and/or by the carrier's or service provider's own requirements or specifications.
In view of this, one can consider cellular telecommunications systems to be “one size fits all” types of systems. All mobile phones operating on a given network are subject to the same constraints, regardless of whether the mobile phone was given to the user for free as part of a particular plan or whether the user paid hundreds of dollars or more for the phone. There is usually no differentiation, and bandwidth and transmission characteristics mentioned above are imposed on all subscribers.
By way of example only, certain manufacturers have offered luxury cellular phones costing many thousands of dollars. Nokia, for one, launched a company called Vertu to sell high end phones. The Vertu Constellation, which is finished in 18 kt gold, retailed for $20,000. An even more expensive phone is the Motorola SLVR L7 Diamond, which was priced at $75,000. And the Diamond Crypto Smartphone has been reported to cost $1.3 million. Nonetheless, in existing systems users of such phones are subject to the same performance problems and constraints as are users of low priced or even free phones.
Vocoder performance is only one aspect that affects quality of service (“QoS”) for a subscriber. As soon as signal leaves a mobile station, it is traveling through many spans and even networks until it reaches its destination, which may be another mobile station. Such transmission characteristics as network availability (which often relates to equipment protection), signal delay, jitter and dropped packets rate are major factors that affect the grade of service quality. In traditional cellular networks, there is no differentiation of users by quality of service.
It may be useful to note that in the literature on wireless communications the term “multi-tier cellular network” usually refers to overlaying cells of different size such as micro-cells and macro-cells in a two-tier network, which are commonly used today. This is not the meaning of “multi-tier” network as it is used herein. A “multi-tier” network as used herein refers to a wireless communication network with different tiers of service, wherein each tier of service corresponds to a different level of service, such as quality of service (QoS) or different levels of security, each tier priced differently. In the literature, such networks are often referred to as “multi-class wireless networks.” For the purposes of this disclosure the terms “multi-tier” and “multi-class” are used interchangeably as synonymous.
In view of the above, a need exists for improved service quality in cellular communications systems and other wireless architectures. A further need exists for a multi-tier cell phone service offering customers guaranteed minimum bandwidth and level of quality of communication (defined also by latency, jitter, and network availability and dropped rate of the calls). Yet another need exists for custom service plans allowing customers to purchase custom level of cell phone communication service, which guarantees a minimum bandwidth and level of quality of communication (defined also by latency, jitter, network availability and dropped rate of the calls), corresponding to a particular tier in a multi-tier communication system. Still another need exists to match the quality of cellular phone communications to the quality and/or price level of a handset used by a customer.